An example of the cryorefrigerator for obtaining cryogenic temperatures by iterating the introduction and expansion of high-pressure refrigerant gas is shown in FIG. 6. A regenerator of this cryorefrigerator employs a magnetic regenerative material such as Er.sub.3 Ni.
FIG. 6 is a sectional view of the cryorefrigerator. This cryorefrigerator is provided with a first displacer 3 which has a first chamber with a regenerative material accommodated therein and which is sealed in a first cylinder 1, and a second displacer 7 which has a second chamber communicating with the first chamber and accommodating a regenerative material and which is sealed in a second cylinder 5. The first chamber of the first displacer 3 is optionally communicated with a high-pressure chamber 12 having an inlet 11 or with a low-pressure chamber 14 having an outlet 13, via a valve stem 9 and a valve 10.
The communication path from the first chamber to the high-pressure chamber 12 or the low-pressure chamber 14 is switched over by rotating the valve 10 by means of a synchronous motor 15.
The cryorefrigerator having the above construction operates as follows.
Referring again to FIG. 6, a high-pressure refrigerant gas fed from a compressor (not shown) or the like is introduced into the first chamber of the first displacer 3 through the inlet 11 and via the valve 10 and the valve stem 9, where the refrigerant gas undergoes heat exchange with the regenerative material within the first chamber, thus being cooled (first stage). The refrigerant gas cooled in this way is then introduced into the second chamber within the second displacer 7, where the refrigerant gas undergoes heat exchange with the regenerative material within the second chamber, thus being further cooled (second stage).
After these processes, the valve 10 is rotated by the synchronous motor 15, so that the first chamber is communicated with the low-pressure chamber 14. Then, the high-pressure refrigerant gas that has been introduced in the first chamber and the second chamber is quickly expanded, resulting in decrease in gas temperature. In this way, heat energy obtained by the expansion of the refrigerant gas is accumulated on the regenerative material.
As described above, a cryogenic temperature is obtained by iterating the introduction of the high-pressure refrigerant gas into the first chamber and the second chamber and its expansion (i.e., by iterating the refrigerating cycle).
In the cryorefrigerator having a structure as shown in FIG. 6, typically, spherical particles 16 of lead (Pb) are filled as a regenerative material on the high-temperature side of the second chamber 6, while spherical particles 17 of Er.sub.3 Ni are filled on the low-temperature side of the chamber, as shown in FIG. 7, in order to enhance the low temperature regenerative efficiency in the second displacer 7.
In the conventional cryorefrigerator, high regeneration efficiency has been obtained by filling the spherical particles 16 of Pb on the high-temperature side of the second chamber 6 and filling the spherical particles 17 of Er.sub.3 Ni on the low-temperature side of the chamber as described above.
In recent years, such a cryorefrigerator as described above has come to be applied in an increasingly wider range. With this trend, there are demands for a cryorefrigerator having an even larger refrigerating capacity and being small in size and light in weight.